Composite panels are well known in the aerospace industry. For example, composite panels may be used to design, build, and/or test components for aircraft. People of skill in the art appreciate that these panels may have a certain void content or percentage of porosity, which, while generally undesirable, is an unavoidable byproduct of the processes used to manufacture the composite panels. The void content of a composite panel may adversely affect several of its properties, including the panel's mechanical and thermal properties. For example, studies have shown that the interlaminar shear strength of panels manufactured from fiber reinforced polymer composite materials decreases by 7% per 1% of voids up to a total void content of about 4%.
To ensure that a composite panel's void content does not exceed a set maximum, the composite panels, after they are manufactured, may be tested by using one or more destructive tests. Determination of the void content of a panel by destructive testing, however, may leave the composite panel unusable for its intended purposes. Thus, some manufacturers may manufacture a “witness coupon” with the composite panel (i.e., they may manufacture a composite panel that exceeds the required length of the panel, and cut off this excess length (the witness coupon) for conducting destructive testing). This too, however, is undesirable, as it leads to wastage of material and unnecessarily increases the cost of manufacturing the panels.
Nondestructive testing techniques for determining the void content of a composite panel have thus, in recent years, gained popularity. U.S. Pat. No. 6,684,701 to Dubois et al. outlines some nondestructive methods for testing for the void content of composite panels. The void content of the panels may be determined, for instance, by using reflected through transmission ultrasound (RTTU) or by through transmission ultrasound (TTU). More specifically, amplitude of an ultrasound wave that has propagated through a composite panel may be compared to the amplitude of an ultrasound wave that has propagated through a reference sample having a known void content. For example, where it is desired that a composite panel have a void content of less than 4%, a reference panel having a 4% void content may be used for comparison with the composite panel. But, manufacturing composite panels having a fixed void content (e.g., for use as a reference panel, or for construction, design, etc.) has heretofore been an arduous task. The present invention discloses systems and methods for creating composite panels having a predetermined, close tolerance, evenly distributed void content.